Ab initio study of the insertion reactions of Sc+(1D) with HF,HCl, H2O,H2S,NH3, PH3, CH4, and SiH4

The mechanism of scandium cation Sc⁺(¹D) insertion into HF, HCl, H₂O, H₂S, NH₃, PH₃, CH₄, and SiH₄ has been investigated by ab initio molecular theory. All these reactions involve the initial formation of intermediate complexes followed by an H‐atom migration process via a transition state to insertion products. The Sc⁺(¹D) insertion into eight compound reactions indicate that (i) the reaction with hydride of the right‐hand group is more exothermic than that of the left‐hand group and has a lower barrier, and (ii) the reaction with the second‐row hydride has a lower overall barrier and is less exothermic than with the first‐row hydride. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Thermal decomposition of ethanol. 4. Ab initio chemical kinetics for reactions of H atoms with CH3CH2O and CH3CHOH radicals

The potential energy surfaces of H-atom reactions with CH(3)CH(2)O and CH(3)CHOH, two major radicals in the decomposition and oxidation of ethanol, have been studied at the CCSD(T)/6-311+G(3df,2p) level of theory with geometric optimization carried out at the BH&HLYP/6-311+G(3df,2p) level. The direct hydrogen abstraction channels and the indirect association/decomposition channels from the chemically activated ethanol molecule have been considered for both reactions. The rate constants for both reactions have been calculated at 100-3000 K and 10(-4) Torr to 10(3) atm Ar pressure by microcanonical VTST/RRKM theory with master equation solution for all accessible product channels. The results show that the major product channel of the CH(3)CH(2)O + H reaction is CH(3) + CH(2)OH under atmospheric pressure conditions. Only at high pressure and low temperature, the rate constant for CH(3)CH(2)OH formation by collisonal deactivation becomes dominant. For CH(3)CHOH + H, there are three major product channels; at high temperatures, CH(3)+CH(2)OH production predominates at low pressures (P < 100 Torr), while the formation of CH(3)CH(2)OH by collisional deactivation becomes competitive at high pressures and low temperatures (T < 500 K). At high temperatures, the direct hydrogen abstraction reaction producing CH(2)CHOH + H(2) becomes dominant. Rate constants for all accessible product channels in both systems have been predicted and tabulated for modeling applications. The predicted value for CH(3)CHOH + H at 295 K and 1 Torr pressure agrees closely with available experimental data. For practical modeling applications, the rate constants for the thermal unimolecular decomposition of ethanol giving key accessible products have been predicted; those for the two major product channels taking place by dehydration and C-C breaking agree closely with available literature data.     

Theoretical study on the substitution reactions of silylenoid H2SiLiF with CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl

DFT calculations at the B3LYP/6-31G(d,p) level have been performed to explore the substitution reactions of silylenoid H(2)SiLiF with XH(n) hydrides, where XH(n) = CH(4), NH(3), H(2)O, HF, SiH(4), PH(3), H(2)S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H(2)SiLiF + XH(n) --> H(3)SiF + LiXH(n-1), which involved the initial formation of an association complex via a five-membered cyclic transition state to form an intermediate followed by the substituted product H(3)SiF with LiXH(n-1) dissociating. These theoretical calculations suggest that (i) there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in the periodic table, and (ii) for the second-row hydrides, the substitution reactions are more exothermic than for the first-row hydrides and the reaction barriers are lower. The solvent effects were considered by means of the polarized continuum model (PCM) using THF as a solvent. The presence of THF solvent disfavors slightly the substitution reaction. Compared to the previously reported insertions and H(2)-elimination reactions of H(2)SiLiF and XH(n), the substitution reactions should be most favorable.     

Extended group function calculations for H2O,NH3 and CH4

Wave functions expressed as antisymmetrized products of strongly orthogonal geminals have been evaluated for H₂O, NH₃ and CH₄. The geminals have been expressed as linear combinations of 2 × 2 detors constructed with localized SCF -MO 's. Several ground state observables have been computed together with the electric polarizabilities and magnetic susceptibilities. In addition, a configuration interaction calculation limited to all possible double group excitations has been carried out.     

Double proton shifts in associates of formic acid with CH4, NH3, H2O,CH3F,NH2F,HOF, and HF molecules

The mechanisms of double synchronous proton transfer in associates of formic acid with solvent molecules of the HC(O)OHX (X = CH₄, NH₃, H₂O, or HF) and HC(O)OHFHY (Y = CH₃F, NH₂F, HOF, F₂, or HF) types have been studied by anab initio (SCF/3G) method. The calculated activation barriers of the reactions are 78.52, 17.72, 9.91, and 7.06 kcal mol^–1 in the former case and 120.1, 259.4, 228.7, 182.8, and 0.35 kcal mol^–1 in the latter case. In the latter case, simultaneously with the double transfer of protons, migration of two fluorine atoms along the chain of the associate occurs.Dedicated to Academician of the RAS N. S. Zefirov (on his 60th birthday).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1690–1700, September, 1995.The present work was carried out with financial support from the Russian Foundation for Basic Research (Project Nos. 93-03-4972 and 93-03-18692) and the International Science Foundation (Grant ISF RNJ 000).     

Reactions of NH+2 ions with H2O and with CH3CHO. Association and exchange reactions involving clusters of the H+(H2O)n(

Kinetic energy dependence of rate constants and branching ratios for reactions of NH₂⁺ ions with water and with acetaldehyde have been studied at 297 K using the drift tube technique. The rate coefficients for two-body and three-body reactions are presented together with the ionized products. Several types are apparent, such as proton transfer, association and exchange reactions.     

Some charge exchange reactions involving H2O

Charge exchange cross sections for the reaction of O⁺, N⁺, and N⁺₂ with H₂O have been measured over the energy range 0.2–10 eV in the center-of-mass system. The implications of these measurements for recent space experiments are discussed briefly.     

Double orbital exponent SCF functions for H2O,NH3, CH4

The results of an investigation on best double orbital exponents for Hydrogen in H₂O, NH₃, CH₄ are reported. An error analysis for calculations with extended basis sets is presented. This analysis is based on the hypothesis that the errors on the integrals are small so that it is possible to use statistical methods.     

Ab initio and variational transition state approach to beta-C3N4 formation: kinetics for the reaction of CH3NH2 with H

The CH3NH2 molecule has been considered as either an important intermediate in methane and ammonia mixtures or a precursor in methylamine and hydrogen mixtures in the synthesis of carbon nitride thin films. The fast Hydrogen (H) abstraction from CH3NH2 is an important process involved in the formation of HCN or CNH in the chemical vapor deposition (CVD) of carbon nitride thin films. The energetic and kinetic characteristics of the H abstraction reaction from CH3NH2 by atomic H used in CVD of beta-C3N4 were studied using ab initio direct dynamics methods for the first time. Two primary processes were identified for this reaction: H abstraction from the CH3 group and H abstraction from the NH2 group. On the basis of ab initio data, the rate constants of each channel have been deduced by canonical variational transition state theory with small-curvature tunneling correction over a wide temperature range of 200 to approximately 3000 K. The theoretical results were compared with available experimental data.     

Theoretical study on the insertion reactions of Ti+(2F) with HF,HCl, H2O,H2S,NH3, PH3, CH4, and SiH4

The insertion reactions of the titanium atom cation Ti⁺(²F) into HF, HCl, H₂O, H₂S, NH₃, PH₃, CH₄, and SiH₄ have been studied by ab initio molecular orbital theory. All these reactions involve the initial formation of an intermediate complex followed by a hydrogen migration process via a transition state to inserting product. The Ti⁺(²F) insertion into eight compounds' reactions show that the reaction with hydride of the right‐hand group is more exothermic than that of the left‐hand group and has a lower overall barrier, and that the reaction with the second‐row hydride has a lower overall barrier and is less exothermic than with the first‐row hydride. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 47–54, 1999     

The complexes of phenyl acetylene with HF,H2O,and NH3: An ab initio study

Phenyl acetylene complexes with HF, H₂O, and NH₃ are investigated with ab initio molecular orbital calculations using the 6-31G Gaussian basis set. HF is found to form a π complex, whereas H₂O and NH₃ form σ complexes. Observations of experimental spectroscopic shifts are rationalized.     

Perturbed SCF MO calculations. Electrical polarizability and magnetic susceptibility of HF,H2O,NH3 and CH4

The perturbation theory is used to evaluate first order SCF corrections upon Roothaan type molecular wave functions due to one-electron perturbations. The method is applied to the one-center SCF MO wave functions of HF, H₂O, NH₃ and CH₄ to calculate the electrical polarizability and the magnetic susceptibility tensors. The results obtained agree reasonably well with the available experimental data. The effects of the limited number of basis functions upon the final results are discussed.

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Zusammenfassung Es werden Störungen erster Ordnung an SCF-MO-Wellenfunktionen, hervorgerufen durch Einelektronenstöroperatoren, im Rahmen der Störungstheorie behandelt. Insbesondere werden die Tensoren der elektrischen Polarisierbarkeit und der magnetischen Suszeptibilität unter Verwendung von Einzentrumfunktionen für HF, H₂O, NH₃ und CH₄ berechnet. Die Ergebnisse werden mit den verfügbaren experimentellen Daten verglichen. Die Effekte der endlichen Basisgröße auf die Resultate werden diskutiert.

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Résumé La théorie des perturbations est utilisée pour évaleur les corrections SCF du premier ordre, aux fonctions d'onde moléculaires du type Roothaan, dûes à des perturbations monoélectroniques. La méthode est appliquée aux fonctions d'ondes SCF MO à un centre de HF, H₂O, NH₃ et CH₃, pour le calcul des tenseurs de polarisabilité électronique et de susceptibilité magnétique. Les résultats obtenus sont en accord raisonnable avec les données expérimentales disponibles. L'effet du nombre limité de fonctions de base sur le résultat est discuté.

     

GF calculation with minimal and extended basis sets for H2O,NH3, CH4 and H2O2

A method is proposed for applying the theory of generalized group functions to SCF-GF calculations with large basis sets. A simple procedure for localising the SCF-MO's resulting from a standard SCF calculation is described, with applications to H₂O, NH₃, CH₄ and H₂O₂. Results compare quite favourably with those obtained by the usual GF method. It is shown that when basis functions are the SCF-MO's and there are only two functions per group, the GF approach is practically equivalent to a configuration interaction treatment where only double excitations within the groups are considered.

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Zusammenfassung Es wird eine Methode zur Anwendung von verallgemeinerten Gruppenfunktionen auf SCF-GF-Rechnungen mit großen Basissätzen vorgeschlagen. Ferner wird ein einfaches Verfahren zur Lokalisierung von SCF-MO's angegeben und auf H₂O, NH₃, CH₄ und H₂O₂ angewendet. Die Resultate sind denen üblicher GF-Methoden ähnlich. Wenn als Basisfunktionen SCF-Funktionen, und zwar nur zwei je Gruppe, angewendet werden, ist der GF-Ansatz praktisch einer CI-Rechnung mit maximal Zweifachanregungen äquivalent.

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Résumé On propose une méthode pour appliquer la théorie des fonctions de groupes généralisés à des calculs SCF GF dans des bases de grande dimension. Un procédé de localisation simple est décrit, il permet de localiser les orbitales SCF ordinaires et est appliqué à H₂O,NH₃, CH₄ et H₂O₂. Les résultats obtenus sont comparables à ceux fournis par la méthode GF ordinaire. Lorsque les fonctions de base sont les O.M. S.C.F. et qu'il n'y a que deux fonctions par groupe, la méthode GF est pratiquement équivalente à une interaction de configuration où seules seraient prises en considération les diexcitations à l'intérieur des groupes.

     

Unimolecular reactions of the isolated immonium ions CH3CH = NH+C4H9, CH3CH2Ch = NH+C4H9 and (CH3)2C = NH+C4H9

The reactions of ten metastable immonium ions of general structure R¹R²C?NH⁺C₄H₉ (R¹ = H, R² = CH₃, C₂H₅; R¹ = R² = CH₃) are reported and discussed. Elimination of C₄H₈ is usually the dominant fragmentation pathway. This process gives rise to a Gaussian metastable peak; it is interpreted in terms of a mechanism involving ion-neutral complexes containing incipient butyl) cations. Metastable immonium ions ontaining an isobutyl group are unique in undergoing a minor amount of imine (R¹R²C?NH) loss. This decomposition route, which also produces a Gaussian metastable peak, decreases in importance as the basicity of the imine increases. The correlation between imine loss and the presence of an isobutyl group is rationalized by the rearrangement of the appropriate ion-neutral complexes in which there are isobutyl cations to the isomeric complexes containing the thermodynamically more stable tert-butyl cations. A sizeable amount of a third reaction, expulsion of C₃H₆, is observed for metastable n-C₄H₉ ⁺NH?CR¹R² ions; in contrast to C₄H₈ and R¹R²C?NH loss, C₃H₆ elimination occurs with a large kinetic energy release (40–48 kJ mol^?1) and is evidenced by a dish-topped metastable peak. This process is explained using a two-step mechanism involving a 1,5-hydride shift, followed by cleavage of the resultant secondary open-chain cations, CH₃CH⁺ CH₂CH₂NHCHR¹R².     

Ab initio study of the reaction of CHO+ with H2O and NH3

An MP4(full,SDTQ)/6-311++G(d,p)//MP2(full)/6-311++G(d,p) ab initio study was performed of the reactions of formyl and isoformyl cations with H₂O and NH₃, which play an important role in flame and interstellar chemistries. Two different confluent channels were located leading to CO+H₃O⁺/NH. The first one corresponds to the approach of the neutral molecule to the carbon atom of the cations. The second one leads to the direct proton transfer from the cations to the neutrals. At 900 K the separate products CO+H₃O⁺/NH are the most stable species along the Gibbs energy profiles for the processes. For the reaction with H₂O the reaction channel leading to HC(OH) (protonated formic acid) is disfavored with respect to the two CO+H₃O⁺ channels in agreement with the experimental evidence that H₃O⁺ is the major ion observed in hydrocarbon flames. According to our calculations, NH+H₂O are considerably more stable in Gibbs energy than NH₃+H₃O⁺;NH will predominate in the reaction zone when ammonia is added to CH₄+Ar diffusion flame, as experimentally observed. At 100 K the most stable structures are the intermediate complexes CO…HOH/HNH. Particularly the CO…HOH complex has a lifetime large enough to be detected and, therefore, could play a certain role in interstellar chemistry. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1432–1443, 1999     

CO2与HCN,NH3,H2O分子络合物的从头计算研究

用ab initio能量梯度法(3-21G基组)分别优化CO_2与HCN、NH_3、H_2O_3个分子络合物的平衡几何构型。结果表明HCN、NH_3和H_2O中的N或O原子与CO_2中的C原子之间形成较弱的范德华键,三者的范德华键键长分别为0.2865、0.2775、0.2543nm,稳定化能分别为14.8、27.0、31.2kJ·mol~(-1),3个分子络合物的构型都呈T型,对3个分子络合物的稳定化能的能量分解研究表明它们的形成主要靠静电作用能。     

Theoretical study on H2 elimination pathways of silylenoid H2SiLiF with CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl

Ab initio molecular orbital calculations have been performed to explore the reaction potential energy surfaces of silylenoid H₂SiLiF with XH _n hydrides, where XH _n = CH₄, NH₃, H₂O, HF, SiH₄, PH₃, H₂S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H₂SiLiF + H-XH _{n − 1} → H _n XSiLiF + H₂, which involves H₂ elimination following the initial formation of an association complex via a four-membered ring transition state to form the substituted three-membered ring silylenoid H _n XSiLiF and a H₂ molecule. This theoretical calculations suggest that (i) for H₂ eliminations there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in periodic table, and (ii) for the second-row hydrides, the H₂ elimination reactions are less exothermic than for the first-row hydrides and the reaction barriers are lower for X–S and Cl. Compared to the insertions of H₂SiLiF into XH _n , the H₂ elimination pathways should be unfavorable with higher barrier and lower exothermic.     

(NH2CH2CH2NH3)4[WⅤO2(OC6H4O)2]2(NH3CH2CH2NH3)·H2O的合成、晶体结构、EPR以及与同构物的比较

Cis-dioxo-catecholatotungsten(Ⅴ) complex (NH₂CH₂CH₂NH₃)₄[W^ⅤO₂(OC₆H₄O)₂]₂(NH₃CH₂CH₂NH₃)·H₂O (1) was synthesized at room temperature by the reaction of tetrabutyl ammonium decatungstate with catechol in the mixed solvent of CH₃OH, CH₃CN and NH₂CH₂CH₂NH₂. The crystal structure of complex was determined by X-ray diffraction structural analysis. The results show that complex belongs to monoclinic system with space group P2₁/c,a=0.712 8(3) nm, b=3.082 3(11) nm, c=0.982 8(4) nm, β=102.639(6)°, V=2.106 8(14) nm³, Z=2, R₁=0.062 8, wR₂=0.183 7. Compared the complex with its analogous complexes (NH₂CH₂CH₂NH₃)₃[Mo^ⅤO₂(OC₆H₄O)₂], it is found that the coordination structure of W have no changes in the processing of electron transfer of tungsten-containing enzymes from the result of the similarity of the EPR spectra of the complexes and flavoenzyme from milk. CCDC: 272937.     

Ab initio calculation for properties of hydrogen bonded complexes H3N⋯HCN,HCN⋯HCN,HCN⋯HF,H2O⋯HF

Self Consistent Field calculations, using TZ+2P basis sets, are reported on four hydrogen-bonded complexes. Vibrational frequencies, rotational constants, infrared and raman intensities are compared with available experimental data. The basis set superposition error is shown not to be important for the calculation of these properties with this basis set.     

Ab initio EOM-CCSD spin-spin coupling constants for hydrogen-bonded formamide complexes: bridging complexes with NH3, (NH3)2, H2O, (H2O)2, FH, and (FH)2

EOM-CCSD spin-spin coupling constants across hydrogen bonds have been computed for complexes in which NH3, H2O, and FH molecules and their hydrogen-bonded dimers form bridging complexes in the amide region of formamide. The formamide one-bond N-H coupling constant [(1)J(N-H)] across N-H...X hydrogen bonds increases in absolute value upon complexation. The signs of the one-bond coupling constants (1h)J(H-X) indicate that these complexes are stabilized by traditional hydrogen bonds. The two-bond coupling constants for hydrogen bonds with N-H as the donor [(2h)J(N-X)] and the carbonyl oxygen as the acceptor [(2h)J(X-O)] increase in absolute value in the formamide/dimer relative to the corresponding formamide/monomer complex as the hydrogen bonds acquire increased proton-shared character. The largest changes in coupling constants are found for complexes of formamide with FH and (FH)2, suggesting that bridging FH monomers and dimers in particular could be useful NMR spectroscopic probes of amide hydrogen bonding.